diff --git a/lib/MC/MCWin64EH.cpp b/lib/MC/MCWin64EH.cpp
index 8bc1f08..3ef1514 100644
--- a/lib/MC/MCWin64EH.cpp
+++ b/lib/MC/MCWin64EH.cpp
@@ -522,7 +522,7 @@
     if (MatchingEpilog) {
       assert(EpilogInfo.find(MatchingEpilog) != EpilogInfo.end() &&
              "Duplicate epilog not found");
-      EpilogInfo[EpilogStart] = EpilogInfo[MatchingEpilog];
+      EpilogInfo[EpilogStart] = EpilogInfo.lookup(MatchingEpilog);
       // Clear the unwind codes in the EpilogMap, so that they don't get output
       // in the logic below.
       EpilogInstrs.clear();